This invention concerns snowshoes and the manner in which snowshoes are secured to boots of users. Specifically the invention relates to use of a more effective, efficient and lower friction buckle with webbing straps in a snowshoe harness, and to a special design of buckle for achieving low friction tightening regardless of the environment of use.
Snowshoes have some form of harness assembly for securely engaging at least the toe end of a user""s boot, normally also including a strap to extend around the heel. Examples of snowshoe harness assemblies are shown in U.S. Pat. Nos. 5,440,827, 5,687,491, 5,699,630, 5,901,471 and copending application Ser. No. 10,199, filed Jan. 21, 1998. A number of snowshoes have webbing type straps in the harness assemblies, formed usually of woven nylon, polyester or other synthetic fibers. These webbing straps are flat, relatively soft and flexible, and have a width of usually about xc2xe inch. Most commonly, a ladder lock type buckle is used for engagement with the webbing straps to tighten the harness over a boot. Ladder lock buckles are common in many different contexts and are based on a type of frictional engagement of the strap, which enters through the bottom of the ladder lock buckle, then passes over a crossbar, doubling back and down under another sharply edged crossbar and extending forward as the tensioned portion of the strap, thus engaging the strap against itself beneath the second crossbar. Other buckles or latches have also been used, such as ratcheting buckles where movement of a lever in one direction advances the toothed strap by one tooth each stroke, and release is effected by an extreme movement of the lever. Such straps are relatively rigid, not webbing straps. The latches are not as quick to use as ladder lock buckles, but greater leverage can be achieved in tensioning the harness.
Ladder lock buckles suffer from the problem of high friction. When the tail end of the webbing strap is pulled to tighten the strap by advancing it through the ladder lock buckle, the sharp fold-back of the strap coupled with the usually somewhat ridged or textured surface of the woven strap, the rubbing against the crossbar, and the rubbing of the strap against itself provide considerable friction and require an objectionable degree of pulling force. Accordingly there is a need for a more easily used buckle for webbing straps, one that provides for much lighter pulling force to reach the tension desired in the tension portion of the strap, while also providing for positive locking engagement of the strap in the buckle, preventing slippage.
Cam lock buckles are well known in contexts other than snowshoes. Heavy metal cam lock buckles have been used for large straps for cargo restraint on a truck or trailer, and buckles based on the same principle have found many other uses. The cam lock buckles, sometimes known spring lever buckles, have a lever with teeth which engage against the webbing strap at such orientation and in such a manner that the greater the back-pulling force in the tensioned portion of the strap, the more the teeth engage into the strap and thus the more positive becomes the locking engagement. The back-pulling of the strap through tension causes the spring lever to tend to pivot more firmly toward the strap and a cross bar beneath the strap, the principle by which the tension causes the teeth to engage more positively into the strap. Some of these cam lock buckles have a generally nautilus-shaped hub, with varying radius and the teeth located at the area of greatest radius. Typically in these cam lock buckles the strap is doubled back over the same bar toward which the spring lever is biased, causing relatively high friction at this doubling over location, friction to be overcome when the strap is to be tightened.
In the invention a snowshoe has a harness with webbing straps, and for tightening the straps and harness on a user""s boot, the strap or straps are fitted with at least one cam lock buckle.
The buckle is connected at one end to the harness and has a second end through which passes a webbing strap to be tightened, with the webbing strap being doubled back through the buckle to provide a tail of the strap for gripping and pulling to tighten the tension portion of the strap leading to the buckle.
The cam lock buckle or spring lever buckle has a spring loaded pivoted lever with engagement teeth on a lower or strap-facing side or edge positioned to engage against the tail of the webbing strap. The buckle includes a cross bar toward which the teeth of the lever are urged such that the tail of the strap passes between the teeth and the bar. In use of the strap and buckle, the webbing strap tail can be pulled through the second end of the buckle freely, forcing the lever to pivot away from the surface of the strap tail against the spring force while the tensioned portion of the webbing strap is pulled tighter to tighten the harness. When pulling force on the strap tail is discontinued, back-pulling force from the tensioned portion of the strap tends to draw the lever more tightly against the strap tail, biting the teeth into the surface of the strap more firmly and thus positively gripping the webbing strap in the buckle and preventing slipping.
In one preferred embodiment the buckle has a direction reversal pin or bar adjacent to and spaced from the spring loaded pivoted lever, between the lever and said one end of the buckle. The webbing strap passes around and over the reversal pin and doubles back such that the strap tail passes between the lever and the cross bar, the reversal pin having a low-friction surface relative to the webbing strap. By this construction, friction in tightening the strap is greatly reduced.
In another preferred embodiment the cam lock buckle is simpler, preferably all plastic with a plastic lever pivotally secured to a plastic frame or base. Teeth preferably comprising lateral ridges on the edge of the lever bite into the strap by spring force, engaging more tightly into the strap when the back-pulling force is present.
It is thus among the objects of the invention to improve the efficiency and ease of use of strap tightening buckles on snowshoes, as well as to provide a particular configuration of cam lock or spring lever buckle which provides for very low friction use. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.